ACE OF BASE: (Singing) She's going to get you. All that she wants is another baby. She's gone tomorrow, boy. All that...

SIMON: We re-discovered all these songs through the radio time machine. That's an online application that's collected the top 20 Billboard hits for each year going all the way back to 1940.

Brett Westervelt created the "Radio Time Machine". He's a graduate student in design at Stanford. And he built the app using Rdio. It's one of the many online music streaming services that gives users a chance to listen to almost any song they want, any time.

BRETT WESTERVELT: Music has kind of gone through this long shift from something that you own and hold in your hands to something that you not only don't hold in your hands but that you actually don't even own, but something that you rent. And so I had this idea to try to design something that would give music a little bit more of a sense of space and time in sort of the digital throwaway age that we live in.

SIMON: And how do people use it?

WESTERVELT: It's been really interesting to watch friends and family uses thing. And I think one surprise for me is that a lot of times people will immediately scan to their birth year. I personally don't have any memories of the music that was playing when I was born but I found myself doing that too, and I think there's something interesting about that. And music kind of kind of connects us with a specific place and time. A common second year that people go to is, you know, senior year of high school.

SIMON: As you listen to all the songs that have popped up, do you notice any trends over the years?

WESTERVELT: Yeah. Definitely. If you start back in the 1940, the first decade of so...

(SOUNDBITE OF SONG "BLUEBERRY HILL")

WESTERVELT: Almost all of the songs are by a musician and his orchestra.

(SOUNDBITE OF SONG "BLUEBERRY HILL")

UNIDENTIFIED SINGER: (Singing) I found my thrill on Blueberry Hill...

WESTERVELT: Those influences change over time and it's really interesting to see Elvis pop up in the '50s and then you see how kind of rock 'n' roll emerges.

WESTERVELT: All along the way music from the past is being kind of brought forward and quoted in various ways but I think that quoting starts to happen more directly as you get into the '90s and you have the emergence of rap and hip-hop. And an interesting occurrence that happened to me the other day was I was listening to the year 1983 and the Police song "Every Breath You Take" came on.

SIMON: Let's pause here for that. (Singing) Da, da, da, da.

(SOUNDBITE OF SONG, "EVERY BREATH YOU TAKE")

POLICE: (Singing) Every breath you take...

WESTERVELT: And then I skimmed forward a little bit and happened to be in the late '90s and all of a sudden that same sample came on the air.

(SOUNDBITE OF SONG, "I'LL BE MISSING YOU")

SEAN COMBS: (Singing) Like they took my friend. I tried a black it out but it plays again.

WESTERVELT: In this case it was Sean Combs song called "I'll Be Missing You." It was written to commemorate the death of Biggie Smalls.

(SOUNDBITE OF SONG, "I'LL BE MISSING YOU")

COMBS: (Singing) Every breath I take. Every move I make.

SIMON: Do you just enjoy playing around with this?

WESTERVELT: Yeah. It's a lot of fun. I think more so though than playing around with it myself, it's been really exciting to get to see other people use this. And as a designer, I think the ultimate dream is to have someone use something that you've created and put out into the world. That's been really what's made this project so exciting to me.

SIMON: Brett Westervelt, creator of the "Radio Time Machine" web application. Thanks so much for being with us.